Jeremy Corbyn has said the SNP is "obsessed" with independence and only his party can keep the Tories out of power.
The Labour leader urged Scottish voters to help him stop the "vicious Tory party" by voting Labour, saying the party was the only opposition which could form a Government - not the SNP.
Labour was all but wiped out in Scotland in 2015, losing 40 of its 41 seats, and recent opinion polls show it struggling in third place on 13% with the Conservatives on 33% and the SNP on 44%.
Speaking at the Scottish TUC conference in Aviemore, Mr Corbyn promised to be the party to "offer hope to the nurse, the teacher, the small trader, the carer, the builder" and - twice - "the factory worker".
He pledged Labour would create a Scottish National Bank, backed by the National Investment Bank, with £20bn of lending power, under Scottish control.
Mr Corbyn promised to restore power to the unions, saying he would repeal the Trade Union Act introduced by David Cameron, which makes it more difficult for workers to take strike action.
He said: "We are standing for the many not the few, and it is through our collective power in a trade union that we ensure the many, standing together, have the power to stand up to the rich and powerful few."
The Labour leader said the SNP was too "obsessed" with fighting Westminster on independence to have enough energy to "transform our economy to ensure no one and no community is left behind".
Mr Corbyn has been buoyed by winning the backing of the Communist Party of Britain, which has announced it will not field any candidates for the first time in history to back the Labour leader.
Instead, members will be "campaigning for a Labour victory as the essential first step towards the formation of a left-led government at Westminster", said Communist general secretary Robert Griffiths.
It comes as the Labour Party was mired in confusion over its stance on retaining Britain's nuclear deterrent.
In an interview on Sunday, the Labour leader refused to confirm whether or not renewal of Trident would be included in the party's manifesto.
However, the party was forced to put out statements saying the commitment to retaining the nuclear deterrent would be in the manifesto, which is expected to be published on 15 May.
Speaking to Sky News on Monday, Defence Secretary Sir Michael Fallon said the confusion showed how "chaotic" Mr Corbyn's leadership was and accused him of being a "security risk" to the UK.
He said the Labour leader's comments had been "staggeringly irresponsible".
Just hours after Mr Corbyn's speech, SNP leader Nicola Sturgeon also addressed the delegates, telling them Scotland would pay a "heavier price" if more Conservatives were elected.
She told voters that the "Tory vision should be ringing alarm bells loudly and clearly across Scotland right now".
"The hardliners have taken over the Tory party and those Tory hardliners now want to take over the country as well.
"It's no surprise that UKIP right now is losing support to the Tories because the Tories are now threatening to take the UK in a direction that UKIP a few years ago could only have dreamed about.
"But it should alarm all of us and, whatever our politics, we should all stand up against that rightward drift of the country that the Tories are determined to effect."
Ms Sturgeon said the election had been called by Theresa May to "strengthen the grip of the Tory Party and to crush dissent and opposition".